Incorrect debit amounts

On the 21st of June I signed a 3 months buy out contract with Rentoza to have 1550 debited from my account for 3 months until the end of August. However 980 was debited at the end of June instead of the agreed amount. I contacted Rentoza before the end of July to have the correct amount debited for July and it was indeed debited and agreed that for August I will pay 1550 plus the outstanding for end of June. I enquired again today to make sure that I will pay end of August as agreed however am being told of 1100 outstanding amount . Where is this amount coming from. I don’t excpecf my account to be debited after August as that is not as per the contract signed. May I have someone call me and fix this mess.